Make AppRunner a singleton and add RunApp helper function

Author: lijy91

examples/window_example/main.cpp

@@ -159,8 +159,7 @@ int main() {
         std::cout << "Display removed: " << event.GetDisplay().id << std::endl;
       });
 
-  AppRunner runner;
-  runner.Run(window_ptr);
+  RunApp(window_ptr);
 
   return 0;
 }

src/app_runner.cpp

@@ -1,3 +1,14 @@
 #include "app_runner.h"
 
-namespace nativeapi {}  // namespace nativeapi
+namespace nativeapi {
+
+AppRunner& AppRunner::GetInstance() {
+  static AppRunner instance;
+  return instance;
+}
+
+int RunApp(std::shared_ptr<Window> window) {
+  return AppRunner::GetInstance().Run(window);
+}
+
+}  // namespace nativeapi

src/app_runner.h

@@ -8,14 +8,21 @@
 namespace nativeapi {
 
 /**
- * AppRunner is a class that manages the application lifecycle and runs the main
+ * AppRunner is a singleton class that manages the application lifecycle and runs the main
  * event loop. It provides a way to run an application with a given window and
  * handle application events.
  */
 class AppRunner {
  public:
-  AppRunner();
-  virtual ~AppRunner();
+  /**
+   * Gets the singleton instance of AppRunner.
+   * @return Reference to the singleton AppRunner instance
+   */
+  static AppRunner& GetInstance();
+
+  // Delete copy constructor and assignment operator
+  AppRunner(const AppRunner&) = delete;
+  AppRunner& operator=(const AppRunner&) = delete;
 
   /**
    * Runs the application with the specified window.
@@ -27,9 +34,22 @@ class AppRunner {
    */
   int Run(std::shared_ptr<Window> window);
 
+
  private:
+  AppRunner();
+  virtual ~AppRunner();
+
   class Impl;
   std::unique_ptr<Impl> pimpl_;
 };
 
-}  // namespace nativeapi
+/**
+ * Convenience function to run the application with the specified window.
+ * This is equivalent to calling AppRunner::GetInstance().Run(window).
+ *
+ * @param window The window to run the application with
+ * @return Exit code of the application (0 for success)
+ */
+int RunApp(std::shared_ptr<Window> window);
+
+}  // namespace nativeapi